change is not a function

### Are you submitting a **bug report** or a **feature request**?

**bug report**

### What is the current behavior?

We received a bugsnag alert about state.change not being a function:
TypeError P.change is not a function

Meanwhile, we at least introduced source maps, so the code mentioned points me to:

### What is the expected behavior?

change should be a function and should only be called if it's a function.

### Sandbox Link

Sadly, I again have no idea how our end users produce the exception.

### What's your environment?

```
"final-form": "4.20.7",
"react": "^17.0.2",
"react-final-form": "^6.5.9",
```

Current chrome, node 18

### Other information

Sorry for again not being able to provide more info - I reported a similar, but different issue in final-form.

Start by reviewing the source-map location shown in the issue and the interaction between final-form 4.20.7 and react-final-form 6.5.9. Try to reproduce the Bugsnag TypeError in the listed React 17 and Node 18 environment; done means identifying a reproducible path and confirming that change is only invoked when callable.

Written by the indexing model from the issue text.